In particular, tissue processors serve to treat tissue samples for the preparation of the tissue samples for a later microscopic examination. For this, the tissue samples are treated with liquids in a process chamber, the so-called retort. In order to achieve a uniform treatment of the tissue samples with the liquids, it is necessary that the liquids have homogeneous properties, in particular a uniform heat distribution, in the process chamber. In order to achieve this, the process chamber is formed as a vessel of a magnetic stirrer, and a stirring body for stirring the liquid contained in the process chamber is arranged in the process chamber, which stirring body can be set in rotation with the aid of a drive unit of the magnetic stirrer. The stirring effect and thus also the time which is required to achieve the desired heat distribution is above all dependent on the design of the stirring body.
One possibility of forming the stirring body is to form the stirring body in the shape of a bar by using a coated bar magnet. In practice, such a stirring body is also referred to as stir bar. When stir bars are used, it is disadvantageous that these move in an uncontrolled manner in the process chamber, that only a low stirring effect is achieved by the stir bars, and that only small forces can be transmitted from the drive unit of the magnetic stirrer to the stir bar.
A further embodiment of the stirring body is to form it such that it comprises two bar magnets and two vanes, the vanes having the form of a semi-ring in cross-section. What is disadvantageous with this embodiment is that, in this embodiment too, only a small force can be transmitted between the drive unit and the magnet, and thus no sufficient adhesive force of the magnets is given. Further, it is disadvantageous that, with this design of the stirring body, a relatively long time is required in order to achieve the desired heat distribution.
EP 1 186 653 A2 shows a bioreactor with a magnetic stirrer. The magnetic stirrer comprises a stirring body in a process chamber of the bioreactor and a drive unit outside the process chamber. The stirring body comprises several magnets which are arranged around magnets of the drive unit.
DE 11 2006 000 814 T5, too, shows a magnetic mixer in which magnets of the stirring body are arranged around magnets of the drive unit.
From DE 20 2004 013 715 U1 a drive device for a stirrer is known, in which again the magnets of the stirring body are arranged around magnets of a drive unit.